As the Senate debates whether to vote this week on the Republicans’ proposed replacement for the Affordable Care Act (ACA), a new study has been released—finding that after the ACA became law in 2011, more women with breast cancer were diagnosed early, in stage 1 of the disease.

Diagnosing breast cancer while it’s still in stage 1 can improve patients’ prognosis and reduce the need for intensive and costly treatments, the study authors wrote in the journal Cancer Epidemiology. And it's likely that such an increase has saved lives, they wrote.

The study analyzed data from more than 470,000 breast cancer patients, ages 50 to 74, who were covered by private insurance or Medicare. All of the women were newly diagnosed with breast cancer either between 2007 and 2009 (before the ACA was in place) or between 2011 and 2013 (after the bill took effect).

Between those two time periods, the percentage of breast cancers diagnosed in stage 1 increased 3.6 percentage points, from 54.4% to 58%. The researchers also found a corresponding decline in stage 2 and stage 3 diagnoses, with no change in the rate of stage 4 diagnoses.

Lead author Abigail Silva, PhD, an assistant professor of public health sciences at Loyola University Chicago Stritch School of Medicine, says she was “pleasantly surprised” to see an effect, although modest, so soon after the ACA was put into place. “It’s really exciting and shows the kind of impact this legislation can have for good,” she says.

The earlier cancer is detected, the more effectively it can be treated. And Silva says there can be a significant difference in the type of treatment needed for stage 1 versus stage 2 cancer.

“In stage 2, it means the cancer has started to spread beyond the breast, to the lymph nodes for example,” says Silva. “In that case a woman might need chemotherapy, which involves longer period of time and more side effects and out-of-pocket costs than, say, the surgery and maybe radiation she’d need for stage 1.”

In the study, increases in stage 1 diagnoses were higher in Latinas and African Americans than in white patients. Historically, minorities are less likely to receive early diagnoses of breast cancer—in part because they’re less likely to get mammograms at recommended intervals, the study authors wrote.

But starting in 2011, the ACA eliminated co-payments and other out-of-pocket costs for mammograms and 44 other preventive services. From 2011 to 2013, rates of early-stage diagnoses were still lower among Latinas and African Americans than they were for white women, but the gap did narrow a tiny bit. (This study did not look at screening rates specifically, but other research has suggested that the ACA has indeed boosted mammogram rates among low-income populations.)

With the exception of skin cancer, breast cancer is the most common cancer among women in the United States, according to the American Cancer Society, with an estimated 253,000 new diagnoses in 2017. “While the shift in stage I cancers was modest, it translates into a potentially significant public health impact,” the authors wrote. “A small shift toward stage I diagnoses would improve the prognosis for thousands of women.”

Silva says previous research suggests that screening behaviors for other types of cancer, including colorectal and cervical, have also improved since the ACA made preventive services (like colonoscopies and Pap tests) free for patients. If these benefits were rolled back—say, if a state elected not to require that preventive services be covered under the Senate’s new legislation—out-of-pocket costs could return and rates could fall back to pre-ACA levels.

“We could be going back to seeing lower screening for diseases that could potentially be diagnosed at earlier stages,” she says. “Not only would that be detrimental to individuals—especially to disenfranchised, low-income individuals—but it would also be more costly for the health-care system as a whole.”